Production shows are done twice on the nights they are presented - an early show meant for late seating and a later show for main seating guests, thus you go to the show after you eat normally 9pm or so. Some shows will only be done once in an evening. In that case they have one show time which will accomodate both dining times - sometimes before early seating, and sometimes it will be one late show at 10Pm or so.

Portofino is DEFINITELY worth the extra cost! We had a fabulous meal, with service to match! I highly recommend it! I would do it again in a heartbeat.
(We scheduled our Portofino dinner for the same time that our normal dining time would have been - 6 p.m.)

p.s. Definitely watch your cruise compass for the showtimes. We didn't realize that on one evening they were only offering one show, and we arrived just as the theater was emptying.